A 1974 memo from Dow Chemical describes several chemicals in a widely used farm fumigant as "garbage." Today, one of those useless chemicals threatens drinking water for more than 1 million people across the San Joaquin Valley.

Now linked to cancer, the toxin was waste from a plastic-making process. Chemical companies often mix such leftovers to create other products to avoid the cost of disposal, says one long-time chemical engineer.

The fumigant manufacturers, Dow and Shell Oil Co., discovered decades ago that 1,2,3-trichloropropane, or TCP, was not effective against worms called nematodes, according to documents in lawsuits filed by a dozen Valley cities against the companies. But they apparently left it in a fumigant anyway.

"TCP was a hazardous waste, not a pesticide," said lawyer Todd Robins, who represents several Valley cities and water agencies. "It did nothing for farmers, but Shell and Dow knowingly used their fumigants as a way to dispose of it."

A Dow representative disputes the lawyer's statement, saying TCP never was intentionally put into the fumigant, called Telone. Nor did the company intentionally allow TCP to remain in the fumigant, he said.

"Rather, from the outset Dow took steps to purify the product through a distillation process," said Randy Fischback of Dow. "Historically, TCP was only occasionally detected in Telone and at extremely low, trace levels."

Shell declined comment, but said it would vigorously defend claims made against it in the TCP lawsuits.

The manufacturers already have agreed to a $13 million TCP settlement for Livingston in Merced County. The city of Clovis is next up in the series of lawsuits. Other cities waiting in line with lawsuits include Stockton, Fresno, Bakersfield, Visalia, Delano and Lamont.

Dow's "garbage" memo is among many documents discovered in the legal action against the chemical companies and distributors. The lawsuits are aimed at forcing the companies to pay for cleaning up the contamination.

Memos and other documents paint a picture of large businesses trying to register the fumigants with the federal government. There is little indication that the companies analyzed possible health hazards in TCP and other so-called inert ingredients.

Today, both state and federal water authorities are moving to regulate TCP. In California, the public health goal is to keep this chemical below one part per trillion -- equal to one drop in 20 Olympic-sized swimming pools.

TCP has been detected at much higher levels in more than 200 Valley drinking water wells. Many small communities and water systems cannot afford the tests to detect the contaminant, so there may be many more tainted wells.

The state is far ahead of the federal government in regulating TCP, which was discovered at a Superfund site in Southern California in the 1990s.

But TCP has the attention of the U.S. Environmental Protection Agency, which expects to have national regulations in the next four to five years.

"It is a carcinogen," said toxicologist Bruce Macler of the EPA drinking water program. "I'm more than just concerned."

For Dow and Shell, it is the second time they have been connected with a hazardous chemical from a fumigant in the Valley's water. In the 1990s, the companies were sued by several cities over a different fumigant called dibromochloropropane or DBCP, which is believed to cause human sterility.

Fresno's DBCP settlement included a payout of $21 million, along with a $2 million trust fund to reimburse the city for maintaining carbon filters on many wells.